Ultrasonic transducers that transmit or receive an ultrasonic wave are employed in diagnosis of a tumor or the like in a human body, nondestructive testing of a structure, sensing of the velocity of a fluid, or the like.
Ultrasonic transducers that utilize vibrations of a piezoelectric entity have been used in the past. With recent advancement of the MEMS technology, a capacitive micromachined ultrasonic transducer (CMUT) having a vibration unit fabricated on a silicon substrate is being developed in earnest.
For example, patent literature 1, patent literature 2, and patent literature 3 have disclosed improvement of reliability in activities of a CMUT. Patent literature 4 has disclosed a method of controlling a center frequency and a bandwidth offered by the CMUT.